THE FLOWER—ITS PARTS AND FORMS
The function of the flower is to _produce seed_. It is probable that
all its varied forms and colours contribute to this supreme end.
These forms and colours please the human fancy and add to the joy of
living, but the flower exists for the good of the plant, not for the
good of man. The parts of the flower are of two general kinds—those
that are directly concerned in the _production of seeds_, and those
that act as _covering and protecting organs_. The former parts are
known as the =essential organs=; the latter as the =floral envelopes=.
[Illustration: FIG. 173.—FLOWER OF A BUTTERCUP IN SECTION.]
=Envelopes.=—The floral envelopes usually bear a close resemblance to
leaves. These envelopes are very commonly of two series or kinds—the
_outer_ and the _inner_. The outer series, known as the =calyx=, is
usually smaller and green. It usually comprises the outer cover of
the flower-bud. The calyx is the lowest whorl in Fig. 173.
The inner series, known as the =corolla=, is usually coloured and
more special or irregular in shape than the calyx. It is the showy
part of the flower, as a rule. The corolla is the second or large
whorl in Fig. 173.
The _calyx_ may be composed of several leaves. Each leaf is a
=sepal=. If it is of one piece, it may be lobed or divided, in which
case the divisions are called =calyx-lobes=. In like manner, the
corolla may be composed of =petals=, or it may be of one piece and
variously lobed. A calyx of one piece, no matter how deeply lobed, is
=gamosepalous=. A corolla of one piece is =gamopetalous=. When these
series are of separate pieces, as in Fig. 173, the flower is said to
be =polysepalous= and =polypetalous=. Sometimes both series are of
separate parts, and sometimes only one of them is so formed.
[Illustration: FIG. 174.—FLOWER OF FUCHSIA IN SECTION.]
_The floral envelopes are homologous with leaves._ Sepals and petals,
at least when more than three or five, are in more than one whorl,
and one whorl stands below another so that the parts overlap. They
are borne on the expanded or thickened end of the flower stalk; this
end is the =torus=. In Fig. 173 all the parts are seen as attached to
the torus. This part is sometimes called the _receptacle_, but this
word is a common-language term of several meanings, whereas torus has
no other meaning. Sometimes one part is attached to another part,
as in the fuchsia (Fig. 174), in which the petals are borne on the
calyx-tube.
=Subtending Parts.=—Sometimes there are _leaf-like parts just below
the calyx_, looking like a second calyx. Such parts accompany
the carnation flower. These parts are =bracts= (bracts are small
specialized leaves); and they form an =involucre=. We must be careful
that we do not mistake them for true flower-parts. Sometimes the
bracts are large and petal-like, as in the great white blooms of
the flowering dogwood: here the real flowers are several, small and
greenish, forming a small cluster in the centre.
=Essential Organs=.—The essential organs are of two series. The outer
series is composed of the =stamens=. The inner series is composed of
the =pistils=.
_Stamens_ bear the =pollen=, which is made up of grains or spores,
each spore usually being a single plant cell. The stamen is of two
parts, as is readily seen in Figs. 173, 174,—the enlarged terminal
part or =anther=, and the stalk or =filament=. The filament is often
so short as to seem to be absent, and the anther is then said to be
_sessile_. The anther bears the pollen spores. It is made up of two
or four parts (known as sporangia or spore-cases), which burst and
discharge the pollen. _When the pollen is shed, the stamen dies._
[Illustration: FIG. 175.—THE STRUCTURE OF A PLUM BLOSSOM.
_se_, sepals; _p_, petals; _sta_, stamens; _o_, ovary; _s_, style;
_st_, stigma. The pistil consists of the ovary, the style and the
stigma. It contains the seed part. The stamens are tipped with
anthers, in which the pollen is borne. The ovary, _o_, ripens into
the fruit.]
The _pistil has three parts_: the lowest, or seed-bearing part,
which is the =ovary=; the =stigma= at the upper extremity, which is
a flattened or expanded surface, and usually roughened or sticky;
the stalk-like part or =style=, connecting the ovary and the stigma.
Sometimes the style is apparently wanting, and the stigma is said to
be sessile on the ovary. These parts are shown in the fuchsia (Fig.
174). The ovary or seed vessel is at _a_. A long style, bearing a
large stigma, projects from the flower. See also Figs. 175 and 176.
Stamens and pistils probably are homologous with leaves. A pistil is
sometimes conceived to represent anciently a leaf as if rolled into
a tube; and an anther, a leaf of which the edges may have been turned
in on the midrib.
[Illustration: FIG. 176.—SIMPLE PISTILS OF BUTTERCUP, one in
longitudinal section.]
[Illustration: FIG. 177.—PISTIL OF GARDEN PEA, the stamens being
pulled down in order to disclose it; also a section showing the
single compartment (compare Fig. 188).]
The pistil may be of _one part or compartment, or of many parts_.
The different units or parts of which it is composed are =carpels=.
Each carpel is homologous with a leaf. Each carpel bears one or more
seeds. A pistil of one carpel is =simple=; of two or more carpels,
=compound=. Usually the structure of the pistil may be determined by
cutting horizontally across the lower or seed-bearing part, as Figs.
177, 178 explain. A flower may contain a simple pistil (one carpel),
as the pea (Fig. 177); _several simple pistils_ (several separate
carpels), as the buttercup (Fig. 176); or a _compound pistil_ with
carpels united, as the Saint John’s wort (Fig. 178) and apple. How
many carpels in an apple? A peach? An okra pod? A bean pod? The seed
cavity in each carpel is called a =locule= (Latin _locus_, a place).
In these locules _the seeds are borne_.
[Illustration: FIG. 178.—COMPOUND PISTIL OF A ST. JOHN’S WORT. It has
5 carpels.]
=Conformation of the Flower=.—A flower that has calyx, corolla,
stamens, and pistils is said to be =complete= (Fig. 173); all others
are =incomplete=. In some flowers both the floral envelopes are
wanting: such are =naked=. When one of the floral envelope series is
wanting, the remaining series is said to be calyx, and the flower is
therefore =apetalous= (without petals). The knot-weed (Fig. 179),
smartweed, buckwheat, elm are examples.
[Illustration: FIG. 179.—KNOTWEED, a very common but inconspicuous
plant along hard walks and roads. Two flowers, enlarged, are shown at
the right. These flowers are very small and borne in the axils of the
leaves.]
Some flowers lack the pistils: these are =staminate=, whether the
envelopes are missing or not. Others lack the stamens: these are
=pistillate=. Others have neither stamens nor pistils: these are
=sterile= (snowball and hydrangea). Those that have both stamens
and pistils are =perfect=, whether or not the envelopes are
missing. Those that lack either stamens or pistils are =imperfect=
or =diclinous=. Staminate and pistillate flowers are imperfect or
diclinous.
[Illustration: FIG. 180.—STAMINATE CATKINS OF OAK. The pistillate
flowers are in the leaf axils, and not shown in this picture.]
[Illustration: FIG. 181.—BEGONIA FLOWERS. Staminate at _A_:
pistillate below, with the winged ovary at _B_.]
When staminate and pistillate flowers are borne on the same plant,
_e.g._ oak (Fig. 180), corn, beech, chestnut, hazel, walnut, hickory,
pine, begonia (Fig. 181), watermelon, gourd, pumpkin, the plant is
=monœcious= (“in one house”). When they are on different plants,
_e.g._ poplar, cottonwood, bois d’arc, willow (Fig. 182), the plant
is =diœcious= (“in two houses”). Some varieties of strawberry, grape,
and mulberry are partly diœcious. Is the rose either monœcious or
diœcious?
[Illustration: FIG. 182.—CATKINS OF A WILLOW. A staminate flower
is shown at _s_, and a pistillate flower at _p_. The staminate and
pistillate are on different plants.]
Flowers in which the parts of each series are alike are said to be
=regular= (as in Figs. 173, 174, 175). Those in which some parts
are unlike other parts of the same series are =irregular=. Their
regularity may be in calyx, as in nasturtium (Fig. 183); in corolla
(Figs. 184, 185); in the stamens (compare nasturtium, catnip, Fig.
185, sage); in the pistils. Irregularity is most frequent in the
corolla.
[Illustration: FIG. 183.—FLOWER OF GARDEN NASTURTIUM. Separate petal
at _a_. The calyx is produced into a spur.]
[Illustration: FIG. 184.—THE FIVE PETALS OF THE PANSY, detached to
show the form.]
[Illustration: FIG. 185.—FLOWER OF CATNIP.]
=Various Forms of Corolla.=—The corolla often assumes very definite
or distinct forms, especially when gamopetalous. It may have a long
tube with a wide-flaring limb, when it is said to be =funnelform=,
as in morning-glory and pumpkin. If the tube is very narrow and the
limb stands at right angles to it, the corolla is =salverform=, as
in phlox. If the tube is very short and the limb wide-spreading
and nearly circular in outline, the corolla is =rotate= or
=wheel-shaped=, as in potato.
A gamopetalous corolla or gamosepalous calyx is often cleft in
such way as to make two prominent parts. Such parts are said to be
=lipped= or =labiate=. Each of the lips or lobes may be notched or
toothed. In 5-membered flowers, the lower lip is usually 3-lobed and
the upper one 2-lobed. Labiate flowers are characteristic of the mint
family (Fig. 185), and the family therefore is called the Labiatæ.
(Literally, labiate means merely “lipped,” without specifying the
number of lips or lobes; but it is commonly used to designate
2-lipped flowers.) Strongly 2-parted polypetalous flowers may be
said to be labiate; but the term is oftenest used for gamopetalous
corollas.
[Illustration: FIG. 186.—PERSONATE FLOWER OF TOADFLAX.]
Labiate gamopetalous flowers that are closed in the throat (or
entrance to the tube) are said to be grinning or =personate=
(personate means _masked_). Snapdragon is a typical example; also
toadflax or butter-and-eggs (Fig. 186), and many related plants.
Personate flowers usually have definite relations to insect
pollination. Observe how an insect forces his head into the closed
throat of the toadflax.
The peculiar flowers of the pea tribes are explained in Figs. 187,
188.
[Illustration: FIG. 187.—FLOWERS OF THE COMMON BEAN, with one flower
opened (_a_) to show the structure.]
=Spathe Flowers.=—In many plants, very simple (often naked) flowers
are borne in dense, more or less fleshy spikes, and the spike is
inclosed in or attended by a leaf, sometimes corolla-like, known as
a =spathe=. The spike of flowers is technically known as a =spadix=.
This type of flower is characteristic of the great arum family,
which is chiefly tropical. The commonest wild representatives are
Jack-in-the-pulpit, or Indian turnip, and skunk cabbage. In the
former the flowers are all diclinous and naked. In the skunk cabbage
all the flowers are perfect and have four sepals. The common calla is
a good example of this type of inflorescence.
[Illustration: FIG. 188.—DIAGRAM OF ALFALFA FLOWER IN SECTION:
_C_, calyx; _D_, standard; _W_, wing; _K_, keel; _T_, stamen tube;
_F_, filament of tenth stamen; _X_, stigma; _Y_, style; _O_, ovary;
the dotted lines at _E_ show position of stamen tube, when pushed
upward by insects. Enlarged. ]
=Composite Flowers.=—The head (anthodium) or so-called “flower”
of sunflower (Fig. 189), thistle, aster, dandelion, daisy,
chrysanthemum, goldenrod, _is composed of several or many little
flowers, or_ =florets=. These florets are inclosed in a more or less
dense and usually green _involucre_. In the thistle (Fig. 190) this
involucre is prickly. A longitudinal section discloses the florets,
all attached at bottom to a common torus, and densely packed in the
involucre. The pink tips of these florets constitute the showy part
of the head.
[Illustration: FIG. 189.—HEAD OF SUNFLOWER.]
[Illustration: FIG. 190.—LONGITUDINAL SECTION OF THISTLE HEAD; also a
FLORET OF THISTLE.]
Each floret of the thistle (Fig. 190) is a complete flower. At _a_
is the ovary. At _b_ is a much-divided plumy calyx, known as the
=pappus=. The corolla is long-tubed, rising above the pappus, and
is enlarged and 5-lobed at the top, _c_. The style projects at
_e_. The five anthers are united about the style in a ring at _d_.
Such anthers are said to be =syngenesious=. These are the various
parts of the florets of the Compositæ. In some cases the pappus
is in the form of barbs, bristles, or scales, and sometimes it is
wanting. The pappus, as we shall see later, assists in distributing
the seed. Often the florets are not all alike. The corolla of those
in the outer circles may be developed into a _long, straplike, or
tubular part_, and the head then has the appearance of being one
flower with a border of petals. Of such is the sunflower (Fig. 189),
aster, bachelor’s button or cornflower, and field daisy (Fig. 211).
These long corolla-limbs are called =rays=. In some cultivated
composites, all the florets may develop rays, as in the dahlia and
the chrysanthemum. In some species, as dandelion, all the florets
naturally have rays. Syngenesious arrangement of anthers is the most
characteristic single feature of the composites.
[Illustration: FIG. 191.—PETALS ARISING FROM THE STAMINAL COLUMN OF
HOLLYHOCK, and accessory petals in the corolla-whorl. ]
=Double Flowers.=—Under the stimulus of cultivation and increased
food supply, flowers tend to become double. True doubling arises
in two ways, morphologically: (1) _stamens or pistils may produce
petals_ (Fig. 191); (2) _adventitious or accessory petals may arise
in the circle of petals_. Both these categories may be present in the
same flower. In the full double hollyhock the petals derived from
the staminal column are shorter and make a rosette in the centre of
the flower. In Fig. 192 is shown the doubling of a daffodil by the
modification of stamens. Other modifications of flowers are sometimes
known as doubling. For example, double dahlias, chrysanthemums, and
sunflowers are forms in which the disk flowers have developed rays.
The snowball is another case. In the wild snowball the external
flowers of the cluster are large and sterile. In the cultivated
plant all the flowers have become large and sterile. Hydrangea is a
similar case.
[Illustration: FIG. 192.—NARCISSUS OR DAFFODIL. Single flower at the
right.]
SUGGESTIONS.—=145.= If the pupil has been skilfully conducted
through this chapter _by means of careful study of specimens_
rather than as a mere memorizing process, he will be in mood
to challenge any flower that he sees and to make an effort to
understand it. Flowers are endlessly modified in form; but they can
be understood if the pupil looks first for the anthers and ovaries.
How may anthers and ovaries always be distinguished? =146.= It is
excellent practice to find the flowers in plants that are commonly
known by name, and to determine the main points in their structure.
What are the flowers in Indian corn? pumpkin or squash? celery?
cabbage? potato? pea? tomato? okra? cotton? rhubarb? chestnut?
wheat? oats? =147.= Do all forest trees have flowers? Explain.
=148.= Name all the monœcious plants you know. Diœcious. =149.=
What plants do you know that bloom before the leaves appear? Do
any bloom after the leaves fall? =150.= Explain the flowers of
marigold, hyacinth, lettuce, clover, asparagus, garden calla,
aster, locust, onion, burdock, lily-of-the-valley, crocus, Golden
Glow, rudbeckia, cowpea. =151.= Define a _flower_.
* * * * *
NOTE TO THE TEACHER.—It cannot be urged too often that _the
specimens themselves_ be studied. If this chapter becomes a mere
recitation on names and definitions, the exercise will be worse
than useless. Properly taught by means of the flowers themselves,
the names become merely incidental and a part of the pupil’s
language, and the subject has living interest.